[macOS] Repeated blank UI with concurrent chats; MessagePort out-of-memory errors (26.908.40834)

What version of the Codex App are you using (From “About Codex” dialog)?

26.908.40834 (build 8881), read from the installed app's Info.plist.
Bundle identifier: com.openai.codex; installed as ChatGPT.app.

What subscription do you have?

Not provided in this report.

What platform is your computer?

Darwin 25.6.0 arm64 arm

macOS 26.6.2 (25G83), Apple Silicon, 24 GiB physical memory.

What issue are you seeing?

The Codex chat area or entire desktop window intermittently becomes blank while several chats are running concurrently. This happens frequently enough to substantially disrupt work.

Read-only inspection of desktop logs on 2026-09-15 found the following diagnostic clues:

Two Composer submit failures, at 2026-09-15T00:18:49.650Z and 2026-09-15T00:18:53.455Z (08:18 in UTC+08:00):

[electron-message-handler] [Composer] submit failed
errorMessage="Failed to execute 'postMessage' on 'MessagePort': Data cannot be cloned, out of memory."
errorName=Error

Repeated UI/layout errors: 1,474 occurrences in a snapshot of that day's logs taken around 14:33 local time:

[electron-message-handler] [desktop-notifications][global-error]
ResizeObserver loop completed with undelivered notifications.

Repeated conversation-state errors: 1,042 occurrences in the same snapshot:

[electron-message-handler] Conversation state not found

The logs also contain repeated hook/started, hook/completed, item/started, and item/completed events for unknown conversations.

These counts cover the day's logs available at the snapshot, not a single blank-screen event. No precise timestamp was captured for the latest blank screen, so the errors are not yet correlated to every occurrence.

What steps can reproduce the bug?

User-observed pattern:

1. Open several Codex chats.
2. Run work in them concurrently.
3. During use, the chat area or whole app window intermittently becomes blank.

This is not a deterministic minimal reproduction. The exact concurrency threshold and triggering operation have not been established. Whether background tasks continue after the UI goes blank is unverified.

What is the expected behavior?

The app should keep the chat area and window visible and responsive during concurrent work. If a message allocation or conversation-state operation fails, the UI should present a recoverable error.

Additional information

• Around 14:32 local time, a post-incident check showed normal macOS memory pressure and approximately 4.3 GB of swap in use. These measurements do not establish the memory conditions at the instant of a blank screen.
• A renderer crash, memory leak, or regression in a particular release has not been confirmed. Please treat the error excerpts as investigation leads, not a root-cause claim.
• Searched existing issues for the exact Data cannot be cloned error and for desktop blank-screen reports; did not establish an exact duplicate.
• The Help Center AI support could not create a case or transfer to a human and directed this report to openai/codex/issues.
• This public report contains a sanitized technical summary. Personal paths, project names, contact email, conversation contents/IDs, credentials, and raw logs are omitted.

Please investigate UI state handling and memory allocation during concurrent chats, and advise whether a fix or workaround is available for this build.

Start with the desktop logs around the Composer submit failures, repeated ResizeObserver errors, Conversation state not found messages, and unknown-conversation events. Reproduce concurrent chats if possible and correlate those signals with a blank window. Done means identifying the failure path and providing a fix or verified workaround for build 26.908.40834.